This invention relates to a light transmission system for a train including a plurality of vehicles which is divided into one or more vehicle groups or compositions.
In the past, signal transmission in a transmission system between the vehicles of a railway train has been made by means of one electric wire per signal in almost all cases. Therefore, the number of wires required for the transmission system of the whole train usually amounts to 100-200 wires, resulting in reduced flexibility, reliability, manageability, and noise-resistance of the system.
Additionally, while the quantity of information as well as the transmission rate of signals transmitted between the vehicles tend to increase with the improvements in recent train control systems for the convenience of passengers, it is gradually getting more difficult to further reduce the above defects to perform signal transmission in a conventional system in which using one transmission path per transmission signal is provided between the vehicles.
For the solution of this problem, there has been proposed a system which multiplexes the signals from respective control apparatuses provided in the vehicles and causes the transmission thereof while largely reducing the number of signal wires passing through the vehicles; more particularly, a light transmission system has been introduced which utilizes an optical fiber cable which is excellent in flexibility and is capable of high speed transmission over a wide band as a signal transmission medium.
Such a conventional light transmission system for a train is illustrated in FIG. 1. The train is formed of end vehicles 10 and 10a, and middle vehicles 12a-12c. One of the end vehicles can be considered as a head vehicle and the other as a tail vehicle according to the moving direction of the train. The end vehicle 10 includes a central station 14 of the light transmission system while the end vehicle 10a includes another central station 16. The middle vehicles 12a-12c each include a respective terminal station 18 of the light transmission system. The central stations 14 and 16 are respectively connected to separate control apparatuses 20 while the terminal stations 18 are respectively connected to separate control apparatuses 22. The central stations are connected to the terminal stations through optical fiber cables 24 and 24a forming a signal transmission path. The terminal stations 18 are disposed in every other vehicle from each end vehicle for the respective transmission paths 24 and 24a for going and returning so that the number of the connection points between the stations does not exceed four in order to suppress the upper attenuation limit at the connections, as disclosed in Japanese Laid-open Patent Application No. 58-31632, published on Feb. 24, 1983.
The end vehicles 10 and 10a respectively include commanding devices 26 and 28 such as a master control or a brake valve which are respectively connected to the central stations 14 and 16.
In FIG. 1, when the train moves in the direction shown by arrow A, the central station 14 of the head vehicle 10 receives from the commanding device 26 a command signal which in turn is transmitted through the terminal stations 18 to the central station 16 of the tail vehicle 10a. The terminal stations 18 and the central station 16 respectively provide the corresponding command signals for the control apparatuses 22 and 20 which provide information of their status to the central station 14 which in turn provides status information as its output to a display portion (not shown) in the front platform of the head vehicle 10. It is to be noted that the central stations 14 and 16 are mutually exchanged in function when the moving direction of the train is opposite to the arrow A in FIG. 1.
Since the central stations 14 and 16 of the light transmission system change their functions in accordance with the moving direction of the train as set forth above, it can be said that one of the central stations in the head vehicle of the train which transmits a driving command signal has a central function while the other of the central stations in the tail vehicle of the train which receives the driving command signal and then provides a corresponding command signal for the control apparatuses has a terminal function. It is to be noted that all the terminal stations only have a terminal function of passing any input signal without any processing thereof.
Next, in the case as shown in FIG. 2, where a system comprising sub-train compositions B and C of five vehicles each as one unit, respectively, combined to form a complete composition D of ten vehicles is introduced, the central station 14 in the head vehicle 10 in the composition B with respect to the moving direction shown by arrow A in FIG. 2 performs the central function while the central station 16 of the tail vehicle 10a of the composition B and the central stations 14 and 16 in the composition C perform the terminal function, respectively.
Therefore, the above described system is disadvantageous in that all of the central stations, except for the head vehicle 10 in the composition B, have to be switched over to the terminal function and also a new transmission path interconnecting the compositions B and C must be provided to drive the train composition D as a unit.